1. Field of the Invention
The present invention relates to a method for analyzing an image of a fundus to detect and analyze the optic disc on the basis of the image of the fundus, and an apparatus for executing that method, and particularly to a method and an apparatus which are suitable for computation of optic disc parameters.
2. Detailed Description of the Related Art
Glaucoma is known as a disease of the visual function. In the examination of glaucoma, it is said that the observation of patient's optic disc on the basis of an image of the fundus is important. In recent years, it has become possible to quantitatively measure the optic disc due to progress in the technology of image analysis.
As one of parameters indicating the size of the optic disc cupping in an image analysis, used is a C/D ration which is a distance ratio between a margin of the optic disc cupping (the optic disc cupping being referred to as a cup) and a margin of the optic disc (the optic disc being referred to as a disc). Usually, the C/D ratio is separately computed as a vertical C/D ratio in the vertical direction and a horizontal C/D ratio in the horizontal direction.
These ratios are computed by the following method. As shown in FIG. 11, the vertical C/D ratio is obtained as a ratio of the average of the sizes of the disc margin and that of the sizes of the cup margin on five meridians of 70.degree. to 110.degree. centered at the center of gravity of the disc and at intervals of 10.degree.. The horizontal C/D ratio is obtained as a ratio of the average of the sizes of the disc margin and that of the sizes of the cup margin on five meridians of 340.degree. to 20.degree. centered at the center of gravity of the disc and at intervals of 10.degree..
However, in the case where, as shown in FIG. 12, there is a cup margin portion 100 in which the degree of edema of the optic disc or coloboma of the optic nerve fiber is relatively low in the,vertical direction, or there is a small coloboma portion 101 of the optic nerve fiber, the vertical and horizontal C/D ratios computed in the above-mentioned method may be largely different from the finding of the oculist in clinic. Further, in the case where the cup is eccentric with respect to the center of gravity of the disc, the C/D ratio computed in the above-mentioned method may be different from the finding of the oculist, thereby producing a problem in that the computation is not sufficient.